The present invention relates to improved polyvinyl aromatic foam materials and to improved processes of preparing such foam materials. Particularly, the present invention relates to improved polyvinyl aromatic foam materials having incorporated therein an effective amount of thermoplastic .alpha.-polyolefins and to processes of preparing such improved foam materials. More particularly, the present invention relates to improved styrene polymer foam materials having incorporated therein a mixture of one or more ethylene polymer materials and one or more copolymers of ethylene and vinyl acetate and to processes of preparing such improved styrene polymer foam materials. Still more particularly, the present invention relates to improved polystyrene foam materials having incorporated therein an effective amount of thermoplastic .alpha.-polyolefins, the source of which is recycled polystyrene foam materials having an .alpha.-polyolefin film intimately adhered thereto, and processes for preparing such improved polystyrene foam materials.
The concept of recovering thermoplastic foam scrap and converting such recovered scrap into a material suitable for use in conjunction with virgin thermoplastic polymer to prepare thermoplastic foam is not new.
In U.S. Pat. No. 2,838,801, a continuous process for making vinyl aromatic polymer foam articles is disclosed. The process provides in part for the collection of foam scraps which are then pressed and heated to obtain a dense sintered material. The sintered material is then heated to melting temperatures, devolatilized and returned in a heat plastified and devolatilized form to the process and into admixture with a quantity of virgin thermoplastic vinyl aromatic polymer and a blowing agent to produce a foam from which said foam aritcles might be cut. Vinyl aromatic polymers include polystyrene, polyvinyltoluene and various copolymers of styrene.
In U.S. Pat. No. 4,255,372, a process for producing polyolefin foam materials is disclosed. The process involves, in part, the addition of comminuted and compressed crosslinked polyolefin foam scraps to an amount of raw polyolefin material to form a mixture which is thereafter converted into polyolefin film material. The term "polyolefins" is disclosed as meaning high-pressure or low-pressure polyethylene, copolymers consisting primarily of ethylene as well as mixtures thereof. Such mixtures include ethylene-propylene copolymers, ethylene-butylene copolymers, copolymers of ethylene and vinyl acetate and the derivatives thereof.
In U.S. Pat. No. 3,682,844, expandable polystyrene particles having 0.5-6 percent by weight ethylene-vinyl acetate copolymer distributed through each particle or bead are prepared. The copolymer in finely divided form is dispersed throughout liquid styrene monomer. The expandable polystyrene particles are then formed by suspension polymerization.
In U.S. Pat. No. 3,520,834, the moldability of a foamable polystyrene is disclosed as being improved by incorporating therein a low-density polyethylene resin. Not more than 30 percent by weight, preferably 5-20 percent by weight, of said low-density polyethylene may be admixed with a foamable polystyrene resin to result in a foamable molding composition. It is preferred to premix the foamable polystyrene resin and the low-density polyethylene resin so as to form a uniform mixture thereof before supplying the mixture to an extruder. The density of the low-density polyethylene is from 0.91 to 0.93 grams per cubic centimeter.
In U.S. Pat. No. 3,398,105, a method for producing expanded polystyrene foam having an average cell diameter of less than 95 microns is disclosed. The polystyrene contains evenly distributed therein from 0.01 to 0.5 percent by weight of a finely divided organic resinous polymer and a specific blowing agent mixture. The organic resinous polymers include divinyl benzene/styrene copolymers, Ziegler polyethylene (density 0.945 grams per cubic centimeter) and Ziegler polypropylene. The blowing agent mixture is a mixture of n-pentane and isopentane containing from 30 to 80 weight percent isopentane based on mixture weight.
In U.S. Pat. No. 3,218,373, organic polymeric compositions containing a predominant amount of styrene polymer and lesser amounts of a partially cross-linked polymer of ethylene and a mono-olefinically unsaturated ester monomer selected from the group consisting of vinyl acetate and a lower alkyl acrylate. In preparing such compositions, the patent teaches that it is essential to first lightly cross-link the ethylene vinyl acetate rubber, and then blend it with styrene. Rubbery ethylene-vinyl acetate copolymer compositions containing 15 to 75 percent by weight of vinyl acetate are suitable and those containing 30 to 65 percent by weight of vinyl acetate are preferred for purposes of this reference. In addition, such copolymer compositions containing about 40 to about 55 percent by weight vinyl acetate, based on copolymer weight, are noted as being of special interest. Cross-linking of the ethylene-vinyl acetate copolymer is obtained by heating said copolymer with up to 2.5 percent by weight thereof of an organic peroxide curing agent.
A number of references teach the recovery of thermoplastic foam scrap material for reuse.
In U.S. Pat. No. 3,344,212, waste styrene polymer foam material is first comminuted to discrete particles of approximately uniform size and shape. The resulting particles are coated with a lubricant and then subjected to a stream of superheated steam or other hot inert gas while the particles are agitated to prevent agglomeration. The heat treatment is continued for a sufficient period of time such that the bulk density of the particles increases to a final bulk density between about 15 to 30 pounds per cubic foot. After the particles are cooled, they can be mixed with fresh feed stock and fed to an extruder or other processing device. Suitable lubricants include alkali metal salts of fatty acids; fatty acid amides; fatty acid esters; and fatty acids.
In U.S. Pat. No. 3,607,999, a particulate thermoplastic resinous foam is disposed on a vibrating cooled surface adapted to convey particles away from the point of application. While the particles are adjacent the vibrating surface, radiant heat in a sufficient quantity to cause the particles to collapse and coalesce is applied. The coalesced material is then removed from the vibrating surface, cooled below its thermoplastic temperature and comminuted to a desired particle size. Polystyrene foam particles are suitable for such processing.
In U.S. Pat. No. 3,723,582, a portion of a generally continuous process for manufacturing articles from foamed thermoplastic polymeric resin sheet with a density of no more than about 3 pounds per cubic foot is concerned with recovery and recycle of foam scrap. The foam scrap is collapsed and densified by the application of pressure thereto, without addition of heat, before the blowing agent in the cells of the foam has been replaced by air. The densified scrap is then granulated to a relatively small particle size so that the resultant material has a sufficiently high density for further processing as in an extruder. The process is disclosed as being useful for reclaiming and reusing foamed polystyrene.
In U.S. Pat. No. 3,795,633, scrap thermoplastic foam, e.g., polystyrene foam, is converted into a continuous, i.e., void-free, solid, usable resin using an extruder which has at least one decompression zone to which vacuum is applied. Prior to extrusion, the scrap is suitably particularized, as by grinding, to average particle diameters of about 1 inch or less, desirably about 5/8 inch or less, preferably in the range of about 1/32 to about 1/2 inch. Following extrusion the extrudate is cooled, after which it can be pulverized or pelletized. In a preferred embodiment, the particularized scrap is premixed with about 5 to about 50 parts by weight virgin resin pellets prior to its entry into the extruder.